Once a b cell has been activated by a specific antigen (an antigen binds to an antigen receptor on the b cell membrane), it will divide, making many copies of itself. this process is known as

The answer is Clonal selection.

In a pre-existing group of lymphocytes, in this case B cells, a specific antigen activates the B cell because it bonded to a specific region of the B cell. This will induce the B cell to proliferate, producing  clones of itself, and each clone will produce antibodies. Then the antibodies will bind to the antigen making it easier for to Antigen to be eliminated.